1. Field of the Invention
The present invention relates to an implantable heart-stimulating device with which it is possible to stimulate both ventricles of a heart, i.e. a bi-ventricular pacer.
The invention also relates to a system including such a device and to the use of the system.
2. Description of the Prior Art
Several different implantable devices for stimulating a heart are known. The devices are normally able to sense the electrical activity of the heart. Some implantable devices are able to deliver stimulation pulses to both the left and right ventricles of the heart, and sometimes also to the left and right atria.
Devices that are able to deliver stimulation pulses to both the left and right ventricles are also called bi-ventricular pacers. Such de-vices can be used to treat patients who suffer from different severe cardiac problems, e.g. patients suffering from congestive heart failure (CHF). CHF is defined generally as the inability of the heart to deliver a sufficient amount of blood to the body. CHF can have different causes. It can be caused, for example, by a left bundle branch block (LBBB) or a right bundle branch block (RBBB). By for example using bi-ventricular pacing, the contraction of the ventricles can be controlled in order to improve the ability of the heart to pump blood. The stimulation pulses to the two ventricles can be delivered simultaneously but it is also known to deliver the stimulation pulses to the two ventricles with a short time delay (VV) between them in order to optimize the pumping performance of the heart.
U.S. Pat. No. 5,720,768 describes different possible electrode positions in order to stimulate or sense the different chambers of the heart.
U.S. Pat. No. 6,070,100 describes that electrodes may be positioned in both the left and the right atrium as well as in the left and the right ventricles.
Another phenomenon known in connection with heart stimulation devices (pacers) is premature ventricular contraction (PVC). PVC means, as the expression suggests, that the ventricle in question contracts too early. The occurrence of PVCs can lead to un-wanted consequences in pacers. For example, a PVC may be sensed by an electrode located in the atrium and thereby be interpreted by the pacer as an atrial event. This may cause so-called pacemaker mediated tachycardia (PMT). This problem has been solved in different manners in pacers having means for sensing and pacing the right atrium and the right ventricle. One known manner of treating this problem is that the pacer, when detecting a PVC, initiates an extended post-ventricular atrial refractory period (sometimes designated +PVARP), i.e. a period during which the atrial channel's sensing is unresponsive.
In bi-ventricular pacers, the situation is more complex, since this kind of pacer usually has more sensing and pacing electrodes, and therefore, more signals are detected or generated by the pacer. Techniques are known, however, for preventing PMT also in bi-ventricular pacers. The document U.S. Publication application 2002/0183792 A1 describes a pacer with an extended PVARP-function, in which a certain ventricular blanking period (designated 430 in the document) is used to prevent an unwanted dual PVC response, which could otherwise occur in a bi-ventricular pacer.
There also exist different manners of operating a bi-ventricular pacer. When an event is detected in one ventricle it is possible to immediately deliver a pacing pulse to the same ventricle or only to the other ventricle or to both ventricles. Sometimes the pacing pulse to the other ventricle is delivered with a time delay (VV), if that ventricle is the ventricle that should be paced later than the first ventricle. For example U.S. Pat. No. 6,466,820 discusses different pacing modes (see in particular column 15, lines 24–39). According to this document, in one manner of operating the device, also a PVC (if it arrives sufficiently late in the cardiac cycle) causes a pacing pulse to be delivered to the other ventricle with the normal programmed VV-delay. However, the document does not disclose any separate time interval for the treatment of PVCs.
Even if PMT caused by sensing a PVC in an atrium is prevented in accordance with the prior art, a PVC may still cause arrhythmic problems. For, for example, a patient suffering from a conduction block (for example a LBBB or a RBBB) PVCs can cause ventricular arrhythmia. Because of the block, the left and right ventricle do not depolarize synchronously as in a healthy heart. Since a PVC means that a depolarization takes place earlier than normally, a more complex situation with different degrees of depolarization in different parts of the heart takes place. This increases the likelihood of arrhythmic episodes.